In particle beam treatment devices, a particle beam (particle ray) emitted after being accelerated by a circular accelerator up to a given energy, is transported through a transport pathway to a particle beam irradiation apparatus placed in an irradiation room. In the particle beam irradiation apparatus, the supplied particle beam is radiated after being formed into a shape matched to an irradiation target. In recent years, for reducing an unwanted dose to normal tissues and for effective utilization of radial rays, attention has been paid to three-dimensional radiation. In the three-dimensional radiation, not only the shape in x-y direction (cross-section perpendicular to a beam traveling direction) is formed by scanning electromagnets, but also the shape in z-direction (the beam traveling direction) is formed by changing the energy.
Here, the following two ways are conceivable how to change the energy; one of which is to change a destination energy due to acceleration by a synchrotron (circular accelerator), and the other way is to cause deceleration by use of a variable range shifter capable of changing its attenuation amount by adjustment of the water-equivalent thickness of its transmissive plate. In order to achieve the three-dimensional radiation, a number of energy stages with one hundred levels, for example, are required. The pitches of these one hundred stages are determined to be the same pitch as a water-equivalent thickness (depth of Bragg peak in water). If these stages are to be achieved solely by changing the acceleration energy of the synchrotron, this results in performing hundred times of emission-adjustments of the synchrotron and adjustments of the transport system, and thus, there is a problem of spending a lot of time. Meanwhile, according to the variable range shifter, the more the thickness increases, the larger the scattering and/or the beam loss becomes, so that it is not desired that the required number (one hundred levels) of energy stages be all achieved solely by the variable range shifter.
In this respect, it is conceivable, for example, that half of the required number of stages (50 stages) are provided by the synchrotron as emission energies, while, with respect to respective intermediate levels therein, they are adjusted by changing the attenuation amount at the variable range shifter. At that time, in order to converge the spread particle beam due to scattering at the time of passing through the variable range shifter, it is conceivable to apply a technology of a particle beam irradiation apparatus in which a four-pole electromagnet is placed (see, for example, Patent Document 1).